The present invention relates to a high pressure pumping device.
The field of application of the present invention is advantageously that of units for supplying fuel to the combustion chambers of an endothermal engine, to which application the following description will refer without entering into general details.
As is known, units for supplying fuel to the combustion chambers of an endothermal engine comprise a fuel manifold within which the fuel to be supplied to the combustion chambers is stored, one or more injectors connected to the fuel manifold and adapted, on command, to supply a predetermined quantity of fuel to each combustion chamber, a fuel storage tank and a high pressure pumping device adapted to take the fuel from the storage tank in order to supply it at high pressure to the fuel manifold.
At present, the high pressure pumping device is formed by a volumetric pump provided with at least one cylinder and with a respective piston mounted in an axially sliding manner in the cylinder in order to define a variable volume pumping chamber and moving under the action of the engine camshaft. The intake of the volumetric pump is connected to the storage tank so that fuel can be suctioned into this pumping chamber, while the pump outlet is connected to the fuel manifold so that fuel can be supplied at high pressure to this manifold.
At its intake and outlet, the pump has respective one-way non-return valves, of which the valve associated with the intake enables fuel to be taken into the pumping chamber and is adapted to remain in the closed position when fuel is supplied from this chamber to the fuel manifold.
In this way, the flow from the volumetric pump is solely a function of the speed of rotation of the camshaft (i.e. the number of revolutions per minute of the engine crankshaft), and, in operation, a quantity of fuel that is greater than the quantity to be supplied to the injectors is supplied to the manifold in a cyclic manner.
Consequently, the above-mentioned supply units make it necessary to use a recycling duct connecting the fuel manifold to the tank so that the surplus quantity of fuel can be returned to the tank or, in any case, upstream of the intake of the volumetric pump. This recycling duct is in particular connected to the fuel manifold by means of a pressure regulator of proportional type which is adapted to prevent the pressure of the fuel in the manifold from exceeding a predetermined threshold value and is adapted to introduce the surplus fuel into the recycling duct.
These known supply units have certain drawbacks connected in particular with the above-described volumetric pumps.
In the first place, given that the manifold is located at a substantial distance from both the tank and the volumetric pump, the recycling duct is very long and is therefore difficult to locate within the engine space. As highly inflammable fuel passes through it, the recycling duct must be disposed in a protected position remote from sources of heat or from cutting components that could compromise its structural integrity.
Secondly, the pumping device must supply at its outlet a pressure such as to ensure both that fuel flows into the manifold and that surplus fuel is returned via the recycling duct, with a substantial waste of energy.
A solution that partially resolves the above-mentioned problems is disclosed in German Patent Application DE 196 44 915.
According to this solution, the valve disposed at the intake of the volumetric pump is formed by an electrovalve whose opening and closing is controlled on the basis of the position of the camshaft. In particular, during an initial phase of delivery, the electrovalve is caused to open for a predetermined period of time, so as to allow a quantity of fuel to flow back through the intake duct and therefore to regulate the flow and pressure of the fuel supplied to the manifold.
This latter solution also has certain drawbacks, however, due chiefly to the fact that the electrovalve must be appropriately designed and produced in order to be applied to the volumetric pump. This is disadvantageous in particular from the economic point of view and may also entail problems of bulk.
The object of the present invention is to provide a high pressure pumping device which resolves the above-described drawbacks and which is, in particular, simple and economic to produce.
The present invention therefore relates to a high pressure pumping device of the type described in claim 1.
The present invention also relates to a unit for supplying fuel to an endothermal engine provided with a high pressure pumping device.
The present invention further relates to a unit for supplying fuel to at least one combustion chamber of an endothermal engine of the type described in claim 9.